Technical Field
This patent Disclosure relates generally to resonant inductive sensors and sensing, such as can be used in sensing position, proximity or physical state or condition.
Related Art
A resonant sensor includes a resonator configured for operation in a resonance state (resonant frequency and amplitude). Sensor electronics drives the resonator with an AC excitation current synchronized with resonator oscillation voltage to maintain resonance (sustained, steady-state oscillation), overcoming a resonator loss factor characterized by a resonator impedance. For example, in the case of inductive sensing, an LC resonator includes an inductive sensing coil that operated at resonance projects a magnetic sensing field, with resonator impedance (loss factor) characterized by a series resistance Rs or equivalent parallel impedance Rp.
Resonant sensing is based on measuring changes in resonance state (resonator oscillation amplitude and frequency) in response, for example, to a conductive target. For example, in case of inductive sensing with an LC resonator, resonance is affected by changes in projected magnetic flux energy output from the inductive sensing coil, such as caused by the eddy current effect associated with a conductive target. Sensor resonator response can be measured as changes in eddy current losses manifested as a change in resonator impedance (loss factor Rs/Rp), or as changes in sensor coil inductance (due to a change in eddy current back emf) manifested as a change in resonator frequency.